An integrating sphere is used for measuring optical properties of a light source. The integrating sphere has a substantially spherical hollow space therein. An inner peripheral surface of the hollow space is subjected to surface treatment so as to diffuse and reflect incident light thereon. In addition, a detector for detecting light reflected inside the hollow space is installed in the integrating sphere. The integrating sphere is designed such that light radiated from a light source installed therein is reflected on the inner peripheral surface of the hollow space and an amount of light is collected in the detector in proportion to the amount of radiated light, thereby enabling to serve as an optical integrator.
Recently, a high-luminance LED capable of being used as a lighting source for illumination has been developed and extensively used for an LCD backlight, a traffic signal, a lighting lamp and the like. In order to use such a high-luminance LED in various fields, it is necessary to measure optical properties of the LED in a temperature range suitable for use conditions. In particular, if electric power is applied to a high-luminance LED installed within a limited space, a large amount of heat is generated and thus rapidly raises the temperature of ambient air as well as the temperature of the LED itself. In addition, according to its use conditions, the LED may be used while a metallic LED substrate is cooled. Furthermore, an LED exhibits greatly different performances depending on how efficient a heat-dissipation structure is upon design of an optical system. Therefore, in order to test optical properties of an LED under the same environment as its actual use conditions, temperature conditions in the hollow space of the integrating sphere are required to be identical with temperature conditions of the actual use conditions. In particular, there is a need for an integrating sphere capable of measuring optical properties while uniformly maintaining the temperature of air around a tested LED installed within a hollow space of the integrating sphere.